U.S. patent number 5,456,718 [Application Number 08/176,769] was granted by the patent office on 1995-10-10 for apparatus for detecting surgical objects within the human body.
Invention is credited to Dennis W. Szymaitis.
United States Patent |
5,456,718 |
Szymaitis |
October 10, 1995 |
**Please see images for:
( Certificate of Correction ) ** |
Apparatus for detecting surgical objects within the human body
Abstract
An apparatus and method detects surgical objects within the
human body where the apparatus includes the surgical object
utilized in surgical procedures including a marker made of a
selected nonmagnetostrictive, soft magnetic material which will
emit known specific selected harmonic frequencies when exposed to
an alternating electromagnetic field. That emission will cause a
change in the alternating electromagnetic field which can be
correlated to the presence of only the selected
nonmagnetostrictive, soft magnetic material.
Inventors: |
Szymaitis; Dennis W.
(Pittsburgh, PA) |
Family
ID: |
26872573 |
Appl.
No.: |
08/176,769 |
Filed: |
January 3, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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977336 |
Nov 17, 1992 |
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Current U.S.
Class: |
128/899; 340/551;
340/571; 600/12; 604/362 |
Current CPC
Class: |
A61B
5/06 (20130101); A61F 13/44 (20130101); G01V
15/00 (20130101); A61B 90/98 (20160201); A61B
90/39 (20160201); A61F 2013/00936 (20130101); A61B
2090/0804 (20160201) |
Current International
Class: |
A61F
13/44 (20060101); A61B 19/00 (20060101); G01V
15/00 (20060101); A61F 13/00 (20060101); A61F
002/02 () |
Field of
Search: |
;340/551,571 ;128/899
;600/3,12,14 ;604/280,286,362 ;623/11 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Prebilic; Paul B.
Attorney, Agent or Firm: Ingersoll; Buchanan Alstadt; Lynn
J.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This is a continuation in part of U.S. patent application Ser. No.
07/977,336 filed Nov. 17, 1992, now abandoned.
Claims
I claim:
1. A detectable surgical object used in surgical procedures
comprising:
a) a surgical object; and
b) a marker attached to the surgical object comprised of at least
one marker comprised of at least one elongated body of a selected
nonmagnetostrictive, soft magnetic material with zero
magnetostriction which will emit known specific intensity of
selected harmonic frequencies when exposed to an alternating
electromagnetic field thereby causing a change in the alternating
electromagnetic field which change can be correlated to the
presence of only the selected nonmagnetostrictive, soft magnetic
material.
2. The detectable surgical object of claim 1 wherein the surgical
object is a surgical sponge.
3. The detectable surgical object of claim 2 wherein the marker is
woven into the sponge.
4. The detectable surgical object of claim 1 wherein the coating is
radio opaque.
5. The detectable surgical object of claim 1 wherein the marker
comprises a soft magnetic amorphous material.
6. The detectable surgical object of claim 1 wherein the marker
comprises a ribbon of soft magnetic amorphous material.
7. The detectable surgical object of claim 1 also comprising a
biocompatible coating encapsulating the marker.
8. The detectable surgical object of claim 1 wherein the marker
comprises at least one fiber of soft magnetic amorphous
material.
9. The detectable surgical object of claim 1 wherein the marker
comprises a soft magnetic crystalline material.
10. The detectable surgical object of claim 1 wherein the marker
comprises a ribbon of soft magnetic crystalline material.
11. The detectable surgical object of claim 1 wherein the marker
comprises at least one fiber of soft magnetic crystalline
material.
12. The detectable surgical object of claim 1 wherein the at least
one elongated body has an aspect ratio of at least 200.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a detection device for surgical objects
within the human body. More specifically the invention relates to a
detection device which responds to an alternating electromagnetic
field.
2. Description of the Prior Art
Despite precautions, surgeons still occasionally leave surgical
objects such as sponges and, less frequently, small surgical tools
in their patients after an operation. Areas which are badly injured
tend to have a great amount of blood which may cover the surgical
objects making the objects hard to locate. Also, objects may find
their way under an organ. This is most likely to occur in surgical
areas such as the abdomen which are large and have many organs.
The prior art discloses use of X-ray opaque material positioned on
the surgical devices in order that after the surgery is completed
and the wound is closed an X-ray can be taken to insure no surgical
objects were left within the patient. Although this detection
method is effective, it is cumbersome. Most operating rooms do not
have X-ray machines. Hence, the patient must be taken to another
room. There the patient often must be moved from his gurney to an
X-ray table for X-rays to be taken. If a surgical object is
detected after an X-ray has been taken, the patient must be
returned to the operating room. Then, the cavity or incision must
be reopened to remove the surgical object and then reclosed. This
second surgery can cause a great deal of trauma to the patient
preventing optimum healing. Examples of surgical sponges which are
marked by radio opaque material are disclosed in U.S. Pat. No.
2,190,432 to Lewison, U.S. Pat. No. 2,698,270 to Mesek, U.S. Pat.
No. 4,185,626 to Jones et at., and U.S. Pat. No. 4,205,680 to
Marshall.
A manual counting of the sponges after the surgery is completed is
also used to prevent surgical objects from being left in body
cavities. This is not a foolproof method. Fatigue, poor
handwriting, and misreading of numbers will occur during operations
lasting 4 to 12 hours when dealing with badly damaged patients.
Consequently, miscounts occur as a result of human error.
Greenberg in U.S. Pat. No. 3,587,583 attempts to overcome the
problems of leaving surgical objects within the body. He proposes
to mark the surgical object with a permanently magnetized material.
A surgeon performs an operation in the normal manner. Before
closing the incision the surgeon probes for the presence of a
surgical object with a magnetic field detector means which
generates an electric signal which is modified in the presence of a
magnetic field. If the marked object is present, the magnetic field
of the magnetic marker is sensed by the magnetic field detector
means which modifies the electric signal. Yet, an operating room
has many types of equipment which generate permanent magnetic
fields. The presence of those fields can activate the magnetic
field detector means giving false detection. Because of its
unreliability in an operating room, Greenberg's device is not a
practical solution to the problem.
In U.S. Pat. No. 5,057,095, Fabian proposes to mark surgical
instruments with a marker adapted to produce identifying signal
characteristics when exposed to an alternating magnetic field. He
discloses three types of resonant markers that are able to resonate
at a certain preselected frequency. The first marker is a
magnetomechanical device comprised of a permanent magnet overlaying
a magnetostrictive metal strip in a plastic housing. The
magnetostrictive strip vibrates when the marker is exposed to an
alternating electomagnetic field and its resonance is detected when
the frequency of the applied field reaches a predetermined value.
However, such devices are very sensitive to pressure and stress
which will inhibit them. Since a body cavity is under some pressure
and the marker may be stressed during surgery, this type of marker
is not reliable for use as a marker for surgical objects. The
second proposed type is an electromechanical circuit comprised of
an air coil, with or without a ferrite core and a resonant
structure such as a piezoelectric crystal. As the first type, this
type of marker can be adversely affected by pressure and stress
because its principle of detection relies on a mechanical
resonance, therefore a piezoelectric crystal type marker is also
unsatisfactory. The third type of marker proposed by Fabian is an
electromagnetic LCR circuit. This type of marker can be either
built out of discreet components or made of a flexible printed
circuit. In the former case, this unit is expensive to build and
bulky and it is impractical for surgical sponges. In the later
case, due to its high electrical resonance frequency this type of
marker can be adversely affected by the presence of metal objects
and conductive media. Because the human body is conductive, it is
also impractical for surgical sponges. Consequently, none of the
markers proposed by Fabian, nor the Greenberg marker, has been
available on the market.
In U.S. Pat. No. 5,045,071 McCormick teaches about the use of
magnetic materials for accurately locating the position of a
catheter which has been inserted into a blood vessel. At column 9,
lines 12-16, the patent cross references U.S. Pat. Nos. 4,416,289;
4,431,005 and 4,445,501 for an explanation of the general method of
detection. At column 5, lines 41-52, the '005 patent explains that
a distortion of the magnetic field indicates the presence of the
catheter. Thus, the McCormick patent teaches that merely a change
in the magnetic field is a sufficient indicator of the position of
the marked object. However, McCormick's measurements can be
affected by the presence of other nearby magnetic and conductive
materials. Hence, McCormick's technique can and likely will provide
"false positives" as to the presence or the position of the marked
object.
Thus, there is a need for a marking method and apparatus for
detecting surgical objects within the human body utilizing a
material that can be readily identified before the patient leaves
the operating suite.
3. Techniques for Detecting Electromagnetic Material
There are different ways of providing and detecting what we can
call generically an "electromagnetic marker." The cited prior art
references all use materials which respond to an electromagnetic
field. In order for a material to respond to an electromagnetic
field and therefore to create "detectable changes" of the
electromagnetic field, a material has to have at least one of the
physical properties of electrical conductivity, moderate to high
magnetic permeability, and magnetrostriction (in general associated
with moderate magnetic permeability). Moderate magnetic
permeability is defined as a permeability comprised of between
5,000 and 20,000 and high magnetic permeability as a permeability
above 20,000. In each case, the response to the electromagnetic
field and, therefore, the creation of "detectable changes" of the
electromagnetic field are heavily dependent upon the geometry and
size of the marker. In addition, the response to the
electromagnetic field depends upon the intensity and frequency of
the electromagnetic field.
In general a magnetic material subject to an electromagnetic field
of known and fixed frequency f.sub.o responds to the applied
electromagnetic field by creating "changes" of the intensity of the
applied field and by creating harmonics of the frequency f.sub.o.
If the material is electrically conductive, it responds by creating
not only "changes" of the intensity of the applied field but also
"changes" of the phase of the field. In addition, if the material
is magnetostrictive, the electromagnetic field creates strains or
stress in the material, and the material responds to it by creating
a frequency-dependent "change" of the intensity and of the phase of
the applied field. Therefore, there are three methods of detection.
First, one can simply look for a change of intensity and/or phase
in an applied magnetic field, a method which can only be used for
detection of the position of an object at a distance comparable to
the size of the object. McCormick uses this method. Second, one
could look for the frequency of the applied field to reach a
predetermined value that is the electromechnical resonance
frequency of the marker. Fabian discloses a magnetomechanical
device which uses this technique. Finally one could look for
particular harmonics generated by a material in the presence of an
applied magnetic field. This method has never been used in a
medical environment. Indeed, the teaching of Heltemes in U.S. Pat.
No. 4,857,891, indicates that the art has generally failed to
recognize that "open-strip" markers made of selected
nonmagnetostrictive materials which generate specific harmonic
frequencies upon application of a unidirectional electromagnetic
field can be used to identify the presence of particular
articles.
Heltemes discloses a Magnetic Marker for Electronic Article
Surveillance Systems having multiple filaments randomly dispersed
in a sheet-like substrate so as to be substantially parallel to the
plane thereof. "The filaments are selected of low coercive force,
high permeability material, and the random orientation results in
certain filaments intersecting with them being magnetically coupled
to other filaments to thereby collect and concentrate lines of flux
associated with an applied field of an EAS system into filaments
parallel to the field."
To take advantage of a high magnetic permeability material a marker
has to be elongated (fiber, long strip, with an aspect ratio
length/square root or cross sectional area of a least 200).
Heltemes complies only partially to this requirement, but randomly
distributes the fibers. In this respect Heltemes defeats this
purpose because the applied electromagnetic field has to be
parallel to the magnetic fibers to generate a high enough level of
high harmonics to be recognized as marker specific. Moreover,
Heltemes' marker is not very well suited for generating high
harmonics. Consequently, Heltemes like others in the prior art,
failed to recognize that markers could be created for detection of
surgical objects which generate specific, detectable, selected
harmonic frequencies.
SUMMARY OF THE INVENTION
I provide a marker for a surgical object which responds to the
presence of an alternating electromagnetic field. That response is
detectable as discrete pulses of radio frequencies. The marker is
comprised of at least one elongated member made of
nonmagnetostrictive, soft magnetic material encapsulated with
biocompatible material. Preferably, the magnetic material is an
amorphous metal. However, crystalline materials can be used if the
encapsulation material has a high flexibility and plasticity.
I further provide a method for detecting a surgical object within
the human body which includes marking the surgical object with my
marker which will emit energy in the form of known frequencies when
it is exposed to an alternating electromagnetic field. Detection is
made using a pulse detection technique similar to that used in
magnetic resonance imaging (MRI), a common and safe diagnostic
procedure. A patient is exposed to an alternating electromagnetic
field of about 3-4 Oe (oersteds) for a specific time. This field
will cause the elongated member to become magnetized and
consequently to generate harmonics of the applied alternating
electromagnetic field. A detector placed near the patient will
detect the reflected waveform from the marker as sharp signal peaks
at the specific frequency of the applied alternating
electromagnetic field.
My marker is particularly useful for surgical sponges. However,
other surgical tools (e.g., forceps, scalpel), plastic or
rubber/polymer surgical implement or equipment used during surgery
(e.g. plastic drain, suction tubes), and implants (e.g., artificial
veins, artificial arteries, knee replacement) may also be
marked.
When the surgical object is a surgical sponge, the marker can be
woven into the sponge. I also provide an improved method of
attaching this device to a surgical sponge. When the surgical
object is a surgical tool such as a forceps, the marker is placed
on the tool with an adhesive means.
In the case where the surgical object is an implant, the method of
detecting the surgical object can be used as a diagnosis of past
medical history of implants. Each type of implant can contain a
specific material or combination of materials that emits a specific
signal that corresponds to that surgical object. Thus, if the
patient is incoherent, the doctor can diagnose the patient's past
medical history of implants.
I prefer to perform the excitation and detection steps prior to the
closing of the surgical incision. I can thereby prevent the usual
infection that would go along with leaving the surgical object
within a body and the trauma which corresponds with reopening the
incision to remove the surgical object.
Other details, objects and advantages of the invention will become
apparent as the following description of a present preferred
embodiment thereof and a present preferred method of practicing the
same proceeds.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings I have shown a present preferred
embodiment of the invention in which:
FIG. 1 is a perspective view partially cut away of a present
preferred marker;
FIG. 2 is a perspective view partially cut away of a second
preferred marker;
FIG. 3 is a perspective view of a surgical sponge having one and
optionally two markers woven through the sponge;
FIG. 4 is a diagram of a detector of my marker;
FIG. 5 is a graph of responses of a detector in the presence of my
marker; and
FIG. 6 is a perspective view of a pair of forceps having a marker
positioned on the exterior handle surface.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIG. 1, my marker 2 is comprised of an elongated body
10 of soft magnetic material which is nonmagnetostrictive. It is
characteristic of many ferromagnetic materials that even the
slightest applied mechanical strain tends to cold work the material
and degrade its permeability and other magnetic properties.
Nonmagnetostrictive magnetic materials are insensitive to strain;
they have the required magnetic properties for my marker while they
are also insensitive to work hardening. Amorphous materials are
very difficult to cold work. Preferably, the material of my marker
is an nonmagnetostrictive amorphous material with very soft
magnetic properties. It should have high magnetic permeability, a
low coercive field and induction saturation should be as high as
possible. One suitable material is sold by Allied under the
trademark "Metglas." The composition of the alloy is recited in
U.S. Pat. No. 4,298,862 to Gregor et al. Thus, for example, Allied
compositions identified as types 2826MB@ or 2705M may be preferably
used. Another suitable amorphous material is Vitrovac 6025Z soft
magnetic amorphous alloy, each said at least one elongate body
being parallel to any other elongate body such that said marker
will emit a spectrum of harmonics which includes detectable high
order harmonics, and sold by Vacuumschmelze GmbH of Hanau, Germany.
Although the marker body could be any dimension and shape, I prefer
to make the elongated body 10 as a ribbon or a strip or a set of
parallel ribbons, strips, fibers or filaments. The elongated
geometry of these members allows me to take advantage of the high
magnetic permeability of the materials. Preferably, the elongated
members will have an aspect ratio (length/square root of cross
sectional area) of at least 200. Such a sufficiently large value
for the aspect ratio will assure generation of a detectable signal
according to the teachings of U.S. Pat. No. 3,665,449. If the
direction of an applied electromagnetic field is essentially
parallel to the marker, and the intensity of the applied
electromagnetic field is greater than a minimum field or threshold,
then the marker will generate high harmonics. That is, the marker
will emit a spectrum of harmonics whose intensity decreases slowly
with the order of the harmonics in the spectrum. In particular, the
9th or the 11th harmonics should be detectable. Other harmonics
could also be detectable. I prefer the ribbon 10 to have a width
less than 2 mm, a thickness ranging between 0.01 to 0.03 mm and a
length of about 5 to 7 cm. Body 10 could be longer or shorter.
The width and thickness of the ribbon 10 can be selected to obtain
flexibility so that when the marker is attached to an object such
as a surgical sponge, it will not adversely affect the flexibility
of the object. I prefer to encapsulate the elongated body with a
polymeric material that is compatible with the human body. Suitable
coating materials are nylon and delfin plastic. The coating 12
prevents the body from oxidizing or reacting with body fluids and
covers any sharp edges or comers of the ribbon 10.
In order to maximize the ratio of the length to the square root of
the cross-sectional area, it has been found desirable that the
material be as thin and as narrow as practical, depending upon
off-setting production cost considerations. It is evident that
fibers possess the required geometry. The metallic fiber which I
prefer to use can be made in accordance with the teachings of U.S.
Pat. Nos. 5,003,291, 5,015,992, 5,015,993 and 5,027,886 by
Strom-Olsen and Rudkowski. These fibers are nonmagnetostrictive,
amorphous magnetic materials with very high magnetic permeability.
Typically the diameter of such fibers ranges between 0.01 and 0.04
mm.
I further provide marking means in the form of a flexible marker
made of fiber laminated between two layers of polymeric materials.
In order for detection to occur, one to approximately ten fibers
should be placed parallel to each other and each fiber should be
approximately 1 to 3 inches in length. Such a multiple fiber marker
assembly is shown in FIG. 2. As shown, the marker of this invention
comprises two layers 23 in the form of a web or ribbon of polymeric
materials. I provide a plurality of fibers 11a, 11b and 11c,
arranged parallel to each other and secured between the two layers
23 by adhesion or lamination means. As mentioned earlier and for
the same reasons, I prefer to make use of a polymeric material that
is compatible with the human body.
However, a marker made of a ribbon or fiber should be less than the
length or the width of the surgical object or not so long that it
would require significant bending or multiple folding for
attachment to the object to be marked. When one is outside this
preferred range, a response signal from the marker will be less
characteristic and therefore more difficult to identify.
Although my markers would be X-ray detectable, one could impregnate
the coating or layers with an X-ray opaque material such as a
barium compound to improve detectability. Another possibility is to
use an X-ray opaque coating material which is currently being used
on medical products. Use of such material not only improves the
detectability of the marker, but should also reduce the time needed
to obtain government and hospital approval of use of the
marker.
One could also use nonmagnetostrictive crystalline magnetic
materials such as Permalloy alloy for the marker body 10. If a
crystalline material is used, the cover layer of polymeric material
should be designed to minimize the transfer of mechanical stress
induced upon bending or folding the marker.
The surgical sponge 4 shown in FIG. 3 is a gauze sponge having a
marker 2 woven throughout the sponge. It is understood that other
means of attachment or securing the marker 2 to the surgical sponge
4 can be used. The marker can be connected to the sponge by means
of pressure, heat, adhesive or the like.
Either the marker of FIG. 1 or the marker of FIG. 2 could be used.
I prefer to use markers which are shorter than a length or a
diagonal of the sponge to avoid bending or folding. Optionally, I
may use a second marker 32, shown in chainline, positioned at a
right angle to the first marker 2. This configuration assures that
the sponge will be detected regardless of its orientation with
respect to the detector. One could use more than two markers on an
object. But, as the number of markers increases the response of the
marked object to a detector will likely be less distinctive.
Therefore, I prefer to use one or two markers positioned as in FIG.
3. This arrangement provides a distinctive response such as shown
in FIG. 5.
It is relatively easy to detect an object marked with my marker.
Once the surgery procedure is completed, the surgeon exposes the
surgical cavity to an alternating electromagnetic field, using the
detection system. Preferably, the patient will be on a nonmagnetic
gurney or examination table. A very low magnetic field of
approximately 3 to 4 Oe is all that is required. Such a field is
relatively easy to establish and will not harm the patient or the
equipment which is normally found in an operating room. If desired
one may use as little as 1.5 Oe and as much as 6 Oe or higher.
However, it is normally not practical to exceed 10 Oe because such
high fields would interfere with other equipment present in an
operating room. This magnetic field will cause the marker body
attached to any surgical objects in the surgical cavity to emit
specific harmonic frequencies corresponding to the selected marker
material. That emission will cause a change in the alternating
electromagnetic field, which change can be correlated to the
presence of only the selected nonmagnetostrictive, soft magnetic
marker material. The detection system can be designed to measure
all changes in the applied electromagnetic field and then look for
the specific change which would be caused by the presence of the
marker. Alternatively, the detection system could be designed to
measure only that change or a surrounding band of changes of the
type which would be caused by the presence of the selected marker
material.
A number of techniques and variety of devices could be used to
detect the presence of the magnetized marker body attached to a
surgical object left in the patient. Those techniques and devices
should be apparent to those skilled in the art. The detection
system circuitry with which the marker 2 is associated can be any
system capable of (1) generating within an interrogation zone an
incident alternating electromagnetic field, and (2) detecting
magnetic field variations at selected harmonic frequencies produced
in the vicinity of the interrogation zone by the presence of the
marker therewithin. Such systems typically include means for
transmitting a varying electrical current from an oscillator and
amplifier through conductive coils that form a frame antenna
capable of developing an alternating magnetic field.
A fairly simple detector is illustrated in FIG. 4. A flat search
coil 14 has a first section 13 wound in a clockwise direction from
points A to B and a second section 15 with the same number of
windings running in a counter-clockwise direction from points B to
C. A frame inductor antenna 16 is placed near the search coil. If
an AC current is passed through the inductor antenna an alternating
magnetic field will be created. That field will induce a voltage
through the search coil. One can detect the voltage from points A
to B and plot it on coordinates 34 in FIG. 5 as a sine wave 23. The
voltage from points B to C can be plotted as a sine wave 25, 180
degrees out of phase from sine wave 25. If the two waves are
plotted simultaneously, they will cancel each other and yield a
straight line over the time-axis. In the event a magnetized marker
moves within the interrogation zone of coil 14 it will change the
AC magnetic field received by the coil 14 and modify waves 23 and
25. For a single marker that modification can be seen as a series
of peaks 27 also shown in FIG. 5 on coordinates 35. The points
along the time-axis where peaks occur depend upon the size and
composition of the marker. If too many markers are used, the peaks
would flatten and approach a sine wave. Therefore, I prefer not to
use more than two markers preferably oriented as in FIG. 3. The
marker produces peaks at particular points along the x-axis. Thus,
the detector looks for a response at those intervals. Only if a
response occurs at the chosen points is a detection made. It is
possible that equipment in the operating room, such as CRT's will
generate electromagnetic fields which will cause a detector
response. However, the chances that such interference will produce
peaks at the selected intervals is small. Hence, false detections
are remote possibilities and they can be eliminated by predetecting
and electronically cancelling the signals of such equipment.
My markers can be used in other surgical equipment such as forceps,
scalpels and hemostats. FIG. 6 shows a pair of forceps 6 which have
a marker positioned along the handle. My markers can also be used
to mark surgical implants. Hence a physician could learn about an
implant in the patient's past medical history using my detection
method. The area under suspicion of an implant will be excited at a
specific frequency. If an implant exists in that area, it will emit
energy over a specific spectrum of frequency which corresponds to
the specific implant material. For this diagnostic process to work,
a standard must be used for all implants. Standard material should
be used for each specific implant differing the material from one
implant to another. In that event, the response will identify the
specific implant.
I have shown and described the present preferred embodiment of the
invention. It is to be distinctly understood that the invention is
not limited thereto but may be otherwise variously embodied within
the scope of the following claims.
* * * * *